Polydiacetylenes may be coloured. Further, for example, it is known that the blue form of poly(10,12-pentacosadiynoic acid) is transformed to the red form in response to various stimuli, e.g. temperature, pH and mechanical stress. This has been utilised to produce colorimetric chemosensors or biosensors, where the perturbation arises due to binding of a given analyte to a receptor covalently attached as a pendant group to the polydiacetylene backbone. Preference is generally for polydiacetylene structures such a liposomes or Langmuir-Schaefer films.
Diacetylenes can be polymerised by irradiation with UV light. The use of a UV laser to cause the marking of a diacetylene has been described in, for example, U.S. Pat. No. 5,149,617. That document also describes how the polydiacetylene can undergo a thermochromic change, e.g. from magenta to red. Thus, a single UV irradiation step is followed by a separate, heating step.
U.S. Pat. No. 4,705,742A discloses differential exposure of a conjugated polyacetylenic compound, to develop a range of colours in a layer on a substrate. The irradiation is with an electron beam, at a wavelength below 200 nm.
WO2006/018640 is based in part on an application of how the effects reported in U.S. Pat. No. 4,705,742A can be controlled, and utilised to achieve multi-colour printing. The publication discloses a method of forming an image on a substrate, which comprises applying to the substrate a combination of a diacetylene and a photoacid or photobase. The diacetylene is polymerised by radiation. 10,12-pentacosadiynoic acid is used in the Examples of this application.